upload_to_sd · Cnc Fluidnc MCP: Risk & Policy

WHAT IT DOES

What upload_to_sd does on Cnc Fluidnc

AI agents use upload_to_sd to create or update resources in Cnc Fluidnc — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Cnc Fluidnc environment.

WHY IT NEEDS A POLICY

Why upload_to_sd needs a policy

This tool creates or stores new data on the CNC controller's SD card, making it a Write operation. Severity is high because malicious or corrupted uploads could cause the CNC machine to execute dangerous operations (collisions, incorrect cutting paths, safety violations), but the primary action is file storage rather than immediate execution.

From the tool's definition Tool uploads a file to the CNC controller's SD card storage. The description states 'Upload a file to the CNC controller', which is a write operation that modifies the controller's persistent storage.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

upload_to_sd Rate-limited

upload_to_sd stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "upload_to_sd": {
      "limits": [
        {
          "counter": "upload_to_sd_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Cnc Fluidnc, so you can run agents against it safely.

FAQ

Questions about upload_to_sd

What does the upload_to_sd tool do? +

Upload a file to the CNC controller. It is categorised as a Write tool in the Cnc Fluidnc MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on upload_to_sd? +

Register the Cnc Fluidnc MCP server in PolicyLayer and add a rule for upload_to_sd: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Cnc Fluidnc. Nothing to install.

What risk level is upload_to_sd? +

upload_to_sd is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit upload_to_sd? +

Yes. Add a rate_limit block to the upload_to_sd rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block upload_to_sd completely? +

Set action: deny in the PolicyLayer policy for upload_to_sd. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides upload_to_sd? +

upload_to_sd is provided by the Cnc Fluidnc MCP server (whitneydesignlabs/cnc-fluidnc-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.